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Hydraulics

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Hydraulics Hydraulics Pumps convert mechanical to hydraulic power. Formulas: Flow: Qap = (DpNp/231)eVp where Qap = actual flow from pump (gph ... – PowerPoint PPT presentation

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Title: Hydraulics


1
Hydraulics
2
Hydraulics
  • Pumps convert mechanical to hydraulic power.
  • Formulas
  • Flow Qap (DpNp/231)eVp
  • where Qap actual flow from pump
    (gph)
  • Dp pump
    displacement (in.3/rev)
  • Np pump speed
    (rpm)
  • eVp volumetric
    efficiency of pump
  • 1 gal 231 in3

3
Hydraulics
  • Torque Tsp ?p Dp/(2p 12 eTp)
  • where Tsp shaft torque of pump
    (lbft)
  • ?p pressure across
    pump (psi)
  • eTp torque
    efficiency of pump
  • Hydraulic power Phyp ?p Qap/1714 (hp)
  • Shaft power Psp Phyp /ePp 2p Tsp Np/33000
  • where ePp
    power(overall) efficiency
  • eVp
    eTp

4
Hydraulic pump example
  • Problem 114 in practice problems.
  • Pump flow desired is 20 gpm with a motor
    speed between 1700 and 2200 rpm. Choose the
    smallest pump.
  • Qap (DpNp/231)eVp
  • Solve for Dp using trial and error.
  • For pump JT02 Dp 231 in.3/gal20
    gpm/(2200 rpm0.91) 2.31 in.3/rev gt 2.0
    in.3/rev and wont pump enough at
    fastest speed.
  • For pump JT03 Dp 23120/(17000.91) 2.99
    in.3 and okay since lowest speed wont over pump
    and we can set speed to deliver 20 gpm using the
    3.0 in.3/rev.

5
Hydraulic pump practice problem
  • Calculate the shaft power to drive the pump
  • for JT03 with data from table of Qap 20 gpm, ?p
    3000 psi system pressure 100 psi pump input
    prressure, and ePp 84.

6
Hydraulic pump practice problem
  • Calculate the shaft power to drive the pump for
    JT03.
  • Pump flow is 20 gpm, system pressure is 3000
    psi, input pressure at pump is 100 psi, and pump
    overall efficiency is 0.84.
  • Psp Phyp /ePp
  • 20 gpm (3000-100)psi/(17140.84)
  • 40.3 hp

7
Hydraulic Cylinder
  • Hydraulic cylinder converts hydraulic power to
    mechanical power.

8
Hydraulics
  • Cylinders
  • Formulas
  • Force to extend Fext ppisApis
    prod(Apis-Arod) (lb)
  • where ppis piston pressure (psi)
  • Apis piston area (in.2)
  • prod rod pressure (psi)
    0
  • Arod rod area (in.2)
  • Force to retract Fret prod(Apis-Arod)
    ppisApis
  • where ppis 0

9
Hydraulics
  • Velocity extend vext 231 Qap/(Apis 12)
    (ft/min)
  • Velocity return vret 231 Qap/
    (Apis-Arod)12
  • Velocity can be defined in terms of extension
    distance and time.

10
Hydraulic cylinder example
  • Calculate the force and velocity to extend if
    system pressure is 1800 psi, cylinder diameter is
    3 in., rod diameter is 1 in., back pressure is 50
    psi and pump flow to cylinder is 15 gpm.
  • Fext ppisApis prod(Apis-Arod) vext
    231 Qap/ (Apis12)
  • 1800 psip(3 in.)2/4
    -50psip(3in.)2/4 - p12/4)
  • 1800 7.07 50(7.07- 0.79)
  • 12,412 lbs
  • vext 231 in.3/gal 15 gpm/ (7.07 in.2 12
    in./ft)
  • 40.85 ft/min. /(60 s/min) 0.68 ft/s

11
Hydraulic cylinder practice example
  • For the previous hydraulic cylinder example,
    calculate the force to retract if back pressure
    is assume zero. Also, calculate the velocity to
    retract.

12
Hydraulic cylinder practice example
  • Fret prod(Apis-Arod) ppisApis where
    ppis 0
  • vret 231 Qap/ Apis-Arod)12
  • Fret 1800 psi ( 7.07 in.2 0.79 in.2)
  • 11,304 lbs
  • vret 231 in.3/gal15 gpm/( 7.07 0.79 in.2)12
    in./ft
  • 45.98 lbft

13
Hydraulics
  • Motors convert hydraulic to mechanical power.
  • Formulas
  • Speed Nm 231 Qap eVm/Dm (rpm)
  • Torque Tm (?p Dm/2p12) eTm (lbft)
  • Power Psm Phym ePm (hp)
  • (Qap ?p /1714) ePm (hp)

14
Hydraulic motor example
  • Calculate the hydraulic motor torque efficiency
    and motor output power from the following data
    Flow is 10 gpm at 1000 psi, motor torque is 1545
    in. lbs, motor speed is 185 rpm, motor
    displacement is 11.5 in.3 per revolution, and no
    back pressure.
  • Tm (?p Dm/2p12) eTm Psm (Qap ?p
    /1714) ePm
  • 2 pTm Nm/33000
  • eTm 1545 in. lb/(12 in./ft)2 p(12 in./ft)
  • (1000 psi11.5 in.3/rev)
  • 84.4
  • Psm 2 p 1545 lbin./(12 in./ft) 185 rpm
    4.54 hp 33000 ftlb/minhp

15
Hydraulic Motor
  • Hydraulic motor converts hydraulic power to
    mechanical power.

16
Hydraulic motor practice example
  • Calculate the overall efficiency of the hydraulic
    motor in the previous example

17
Hydraulic motor practice example
  • Psm Phyp ePm
  • (Qap ?p /1714) ePm (hp)
  • ePm 4.54 hp/ (10 gpm1000psi/1714) hp
  • 77.8
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